An AMOLED (Active Matrix Organic Light-Emitting Diode) is able to emit light as it is driven by a current generated by a driving TFT (Thin Film Transistor) in saturation. Different TFTs may have different threshold voltages and may generate different driving currents due to their different threshold voltages when a same gray level voltage is input, thus rendering the nonuniformity of the driving currents. Under the LTPS (Low Temperature Poly-silicon) manufacturing process, the threshold voltages Vth of TFTs have a poor uniformity and may have drifts as well, such that the uniformity in luminance of the AMOLED adopting the conventional 2T1C circuit is always poor. Another factor which has an effect on the uniformity in brightness lies in that the power supply line has an internal resistance and OLED (Organic Light-Emitting Diode) is a light emitting device driven by a current, a voltage drop is generated on the internal resistance of the power supply line when there is a current flowing through OLED, which renders that power supply voltages at different locations cannot reach the required voltage.
In addition, aging problem of OLED is a common problem that all of the OLED light-emitting displays have to be faced with. DC driving is mostly adopted in the prior art, wherein the transmission directions of holes and electrons are fixed, the holes and electrons are injected to a light-emitting layer from a positive pole and a negative pole, respectively, and then excitons are formed in the light-emitting layer to radiate luminescent. Redundant holes (or electrons) which are not combined are accumulated at an interface between a hole transmission layer and the light-emitting layer (or an interface between the light-emitting layer and an electron transmission layer), or flow to the pole across potential barrier. With prolong of the operation time, carriers not combined but accumulated at internal interfaces of the light-emitting layer allow that an built-in electric field is formed inside the OLED, which renders that the threshold voltage of the OLED increases continuously, the luminance of the OLED decreases continuously, and the energy utilization efficiency of the OLED decreases continuously. An AC driving circuit of OLED has been proposed in the prior art, which achieves AC driving for the OLED and solves the aging problem of the OLED, but cannot remove the effect of the internal resistance of the power supply line and the threshold voltage of the driving transistor on the display nonuniformity of the AMOLED.